The United Nations Children's Fund is kicking off a yellow fever vaccination campaign in Ivory Coast despite growing instability and hostility to U.N. staff following a disputed presidential election in November.

UNICEF plans to vaccinate more than 800,000 adults and children in north-central Ivory Coast against yellow fever over the next week.

Health workers will target four rural districts, including Katiola and Béoumi where 66 cases of the mosquito-borne illness have been recorded since November, including 25 deaths.

UNICEF says just one case of the highly deadly disease constitutes an epidemic.

UNICEF spokesman in Ivory Coast, Louis Vigneault-Dubois, said the vaccination campaign was delayed by the tense political gridlock that has gripped the country since a November 28 presidential poll.

"Now it has reached a point where it is urgent to vaccinate the people, to stop the epidemic in the four districts that are concerned by the current campaign and to make sure that the disease does not spread further beyond the four districts that are concerned," said Vigneault-Dubois.

Incumbent president, Laurent Gbagbo, continues to cling to power, though the United Nations and much of the international community have recognized challenger, Alassane Ouattara, as the winner of the election.

The U.N. Mission in Ivory Coast has increasingly come under attack. Last week, at least six U.N. vehicles were attacked by mobs and security forces loyal to Mr. Gbagbo.

This week, the U.N. Security Council boosted its peacekeeping force in Ivory Coast to 12,000 troops, though Mr. Gbagbo demanded the force leave Ivory Coast last month.

Mr. Gbagbo announced Friday that all U.N. vehicles are subject to search, a move U.N. officials have rejected as against international law.

UNICEF's Vignault-Dubois said security is a concern for the vaccination campaign.

"The security situation has significantly deteriorated for everyone in Cote d'Ivoire since early December," he said. "Now, we have not had any attacks on UNICEF personnel right now, so that is the difference."

UNICEF says general instability is keeping 800,000 children out of school and warns that rising food prices could affect the nutritional status of children from poor families.